1. Field of the Invention
The present invention relates to rubber particles for resin reinforcement which are superior in weather resistance and heat stability and to a reinforced resin composition containing these particles.
2. Description of the Prior Art
A resin reinforced with rubber, viz. a high impact resin having superior mechanical strength, is used in a wide variety of application fields.
In order to reinforce a resin effectively with rubber, it is necessary, as represented by ABS resin and HIPS (high impact polystyrene) resin, that the rubber in a particle form be controlled within a specific range of particle sizes and cross-linked moderately as well as being made compatible with the matrix resin by grafting a resin ingredient identical or compatible with the matrix resin onto the rubber so as to disperse the particles of the rubber uniformly in the matrix resin.
Rubbers of the polybutadiene family (unsaturated rubbers), which are easy to cross-link and have a high graft receptive activity, are used extensively as rubbers suitable for the above purpose.
However, the rubbers of this type, because of having unsaturated bonds contained therein, have the drawback of inferior heat stability and weather resistance. Hence these rubbers exhibit deterioration in physical properties during high-temperature processing and the practical use of these rubbers for such purposes is restricted.
The addition of antioxidant and/or ultraviolet absorber to a resin is generally considered for the improvement of its heat stability and/or weather resistance. However, this addition causes a reduction in impact resistance as well as a rise in cost, and there is a question concerning the permanence of its effect.
On the other hand, attempts have been made to reinforce resins with a rubber which does not have a polymer grafted thereto. Japanese Patent Application Kokoku No. 61-46493 discloses a method comprising cross-linking a rubber of a styrene-butadiene block copolymer (SB block copolymer) type, and forming the cross-linked rubber into particles, which are then used to improve the impact strength of aromatic monovinylidene polymers. This method, however, still leaves problems in that the rubber used in this method still contains double bonds, and consequently is inferior in heat stability and weather resistance, and the effect of the improvement of the impact resistance is limited.